CpE 272 Digital Logic Laboratory
Lab #1
Introduction to Basic Logic Gates
Fall 2007
Introduction to Digital Logic:
Digital is a word that means discrete. In this course, digital signals will take on
only two values. This binary nature allows logic to be performed electronically. In this
lab we will be concerned with TTL logic gates. In TTL implementation, a signal between
0 and 0.8 volts is termed ‘false’ and a signal between 2.4 and 5 volts is termed ‘true’.
This allows one to design circuitry to implement the desire logical function.
The following terms are used interchangeably when describing a digital signal.
True=One=High For TTL > 2.4V
False=Zero=Low For TTL < 0.8V
In this lab, you will experimentally verify the Truth Table for the AND gate, OR
gate, NOT gate, NAND gate, NOR gate, XOR gate and find the Truth Table for the given
combinations of logic gates. In your report, you will be asked to show the logic
representation, algebraic expression and truth table for each task.
Wiring Guidelines:
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Connect a wire from the plus five volts to the bus with a red line and a wire from
ground to the bus with a blue line. This will now allow you to have a more
organized proto board.
When placing your chips have them lay over the large gap in the middle of the
proto board.
Make sure to connect the Vcc pin to five volts and the ground pin to ground for
every chip!
Color code as much of your circuit as possible this will help in debugging the
circuit at a later time.
Part I
The connection diagram (with logic representation shown), the algebraic expression and
the Truth Table for the 7408 AND gate are given next.
Experiment 1: Verify the AND gate is working properly by determining its truth table
by connecting the inputs to two switches and the output to a LED.
Experiment 2: Connect the output from the first AND gate into the input of a second
AND gate and connect the third input to the buses. Determine the Truth Table and the
logic representation for this network in your lab notebook. Demonstrate this to your
instructor. In the report explain what you have built in this experiment.
Part II
The connection diagram (with logic representation shown), the algebraic expression and
the Truth Table for the 7432 OR gate are given next.
Experiment 1: Verify the OR gate is working properly by determining its truth table by
connecting the inputs to two switches and the output to a LED.
Experiment 2: Connect the output from the first OR gate into the input of a second OR
gate and connect the third input to the buses. Determine the Truth Table and the logic
representation for this network in your lab notebook. Demonstrate this to your
instructor. In the report explain what you have built in this experiment.
Part III
The connection diagram (with logic representation shown), the algebraic expression and
the Truth Table for the 7404 NOT gate are given next.
Experiment 1: Verify the NOT gate is working properly by determining its truth table
by connecting the inputs to two switches and the output to a LED.
Experiment 2: Connect the output from the first NOT gate into the input of a second
NOT gate. Determine the Truth Table and the logic representation for this network in
your lab notebook. Demonstrate this to your instructor. In the report explain what you
have built in this experiment.
Part IV
The connection diagram (with logic representation shown), the algebraic
expression and the Truth Table for the 7400 NAND gate are given next.
Experiment 1: Verify the NAND gate is working properly by determining its truth table
by connecting the inputs to two switches and the output to a LED.
Experiment 2: Connect both the inputs of the NAND gate together and apply one
signal to them. Determine the Truth Table and the logic representation for this
network in your lab notebook. Demonstrate this to your instructor. In the report
explain what you have built in this experiment.
Experiment 3: Construct an AND gate using only NAND gates. Determine the Truth
Table and the logic representation for this network in your lab notebook. Demonstrate
this to your instructor.
Part V
The connection diagram (with logic representation shown), the algebraic expression and
the Truth Table for the 7402 NOR gate are given next.
Experiment 1: Verify the NOR gate is working properly by determining its truth table
by connecting the inputs to two switches and the output to a LED.
Experiment 2: Connect both the inputs of the NOR gate together and apply one signal
to them. Determine the Truth Table and the logic representation for this network in
your lab notebook. Demonstrate this to your instructor. In the report explain what you
have built in this experiment.
Experiment 3: Construct an OR gate using only NOR gates. Determine the Truth
Table and the logic representation for this network in your lab notebook. Demonstrate
this to your instructor.
Part VI
The connection diagram (with logic representation shown), the algebraic expression and
the Truth Table for the 7486 XOR gate are given next.
Experiment 1: Verify the XOR gate is working properly by determining its truth table
by connecting the inputs to two switches and the output to a LED.
Experiment 2: Connect both the inputs of the XOR gate together and apply one signal
to them. Determine the Truth Table and the logic representation for this network in
your lab notebook. Demonstrate this to your instructor. In the report explain what you
have built in this experiment.
POST LAB QUESTIONS:
1. In Part IV, Experiment 2 you were asked to connect two NOT gates in series. Explain
the reason that you might use this circuit.
2. When a 'false' input is desired, why should you connect this to ground instead of just
leaving the input disconnected?
3. How much current can the 7400 NAND output provide in the high state?
4. On the NI ELVIS, a resistor pack was connected in series with the LEDS on the board.
Why?
5. What two logics are considered the most versatile logic gates?